Michigan was hit with a 4.2 magnitude earthquake on Saturday, the second-strongest in the state’s recorded history, the U.S. Geological Survey (USGS) reported.
There have been no reports of damage or injuries, though the earthquake was big enough that it was reportedly felt in parts of Ohio, Indiana, Illinois, and Wisconsin. A 4.2 quake is not terribly large — people indoors are expected to feel to movement, and hanging objects might swing back on forth.
Still, the event was decidedly unexpected. Michigan is rarely ever affected by seismic activity. According to the USGS, the area where Saturday’s quake occurred has just a 6 to 10 percent chance of any seismic activity in the next 50 years. And if Michigan is impacted by an earthquake, it’s not expected to be very strong — the state’s strongest recorded event was in August 1947, a 4.6 magnitude in almost the exact same location.
It’s difficult to pinpoint the cause of an earthquake so soon after it has occurred, and the USGS has indicated that they believe Saturday’s quake happened naturally and was not the result of fracking or wastewater injection.
But the event occurred amid very recent warnings from scientists and the U.S. government about the increasing likelihood of earthquakes across the central and eastern United States, due in large part to oil and gas operations. Just last week, the USGS reported that earthquakes caused by oil and gas activity — specifically, the practice of injecting wastewater underground — “are occurring at a higher rate than ever before and pose a much greater risk to people living nearby.”
Those human-induced earthquakes are expected to get stronger as the process of wastewater injection continues to increase alongside oil and gas drilling. The popular but controversial process of hydraulic fracturing, or fracking, produces significantly more wastewater than conventional drilling, which results in more underground injections.
Michigan itself does have fracking, but most of its operations are in the northern part of the state, away from where Saturday’s quake occurred.
Right now, seismologists have said the more notable thing about Saturday’s quake is that it may point to previously undiscovered faults in the state. That is important for general hazard planning, but also could be important for future planning of oil and gas operations in Michigan.
As the link between wastewater injection and earthquakes has become stronger, states have been urged to be more careful when drillers are operating near known faults. Ohio’s government has been relatively proactive about this, requiring oil and gas companies to install earthquake monitors before drilling within three miles of a known fault line, or in any area that has ever experienced an earthquake greater than a 2.0 magnitude.
Recently, Oklahoma has been forced to take this into consideration as well, as human-induced quakes there have rapidly increased. Though it has not laid out requirements for oil and gas companies drilling near faults, Oklahoma’s government announced last week that it would officially embrace that large body of scientific research connecting its seismic activity to wastewater injection, and start figuring out how to deal with it.
This article has been updated to reflect the correct date of the earthquake. It was Saturday, not Friday.